Fluorescence based extracellular enzyme activity assay for early detection of biofouling in seawater desalination systems

A method for detecting membrane fouling comprising the steps of:

• providing a membrane fouling sensor positioned adjacent to a feed solution stream in a membrane filtration system wherein a portion of a feed solution stream flows through the sensor contacting a membrane therein;
• said membrane fouling sensor having an inlet valve directing the feed stream to the sensor and an outlet valve directing the feed stream from the sensor unit back to the main feed stream proximal to the main filtration unit;
• allowing the feed solution stream to contact the membrane fouling sensor during the normal operation of the membrane filtration system, such that the sensor membrane is subject to substantially the same conditions as the membrane in the membrane filtration unit;
• operating the membrane filtration system to for a time period ranging from 1 hour to 100 hours, during which time the sensor membrane and the membrane in the membrane filtration unit are exposed to any microorganisms in the feed solution stream and said microorganisms may adhere to the sensor membrane and membrane the membrane in the membrane filtration unit membranes causing one or more biofilm to develop on the membranes and producing extracellular enzymes;
• creating a closed system in the membrane fouling sensor by closing the inlet and outlet valves thereby trapping a portion of the feed stream and any microbial extracellular enzymes in the membrane fouling sensor;
• injecting a fluorogen-substrate into the membrane fouling sensor via an inject port positioned distal to the inlet valve and proximal to the membrane;
• allowing the fluorogen-substrate to contact the feed stream and any microbial extracellular enzymes trapped in the sensor for 1-60 minutes;
• removing a portion of the feed stream trapped in the sensor via the flush port;
• using a fluorometer to measure the removed portion of the feed stream for fluorescence produced from the fluorogen-substrate interaction with extracellular enzymes;
• correlating the measured fluorescence with extracellular enzyme activity in the sample;
• and using the correlation to determine a biofouling level of the membranes.

A membrane fouling sensor comprising:

• a sensor unit positioned adjacent to a main feed solution stream proximal to a main membrane filtration unit in a membrane filtration system, said sensor unit having a filtration membrane;
• an inlet valve positioned at the main feed stream that diverts a portion of the main feed stream to the sensor unit as a sensor feed stream when opened and prevents the main feed stream from entering the membrane fouling sensor when closed;
• an outlet valve that directs the sensor feed stream back to the main feed stream distal to the inlet valve and proximal to the main membrane filtration unit when opened and retains the sensor feed stream in the membrane fouling sensor when closed,
• a feed stream conduit positioned between the inlet valve and the outlet valve that directs the feed stream from the inlet valve to the outlet valve through the sensor unit,
• an inject port in the feed stream conduit distal to the inlet valve and proximal to the sensor unit;
• and
• a flush port in the feed stream conduit distal to the sensor unit and proximal to the outlet valve.

A method of detecting biofouling of a membrane comprising the steps of:

• collecting a sample of a permeate from a membrane filtration system, said permeate resulting when a feed stream solution has been filtered by the membrane;
• selecting a fluorogen-substrate comprising Methylumbelliferone (MUF) that can be cleaved by one or more microbial extracellular enzymes;
• mixing the permeate sample with the fluorogen-substrate;
• using a fluorometer to measure fluorescence produced by the interaction of one or more microbial extracellular enzymes in the permeate sample on the fluorogen-substrate;
• and
• correlating the fluorescence of the permeate sample and fluorogen-substrate mixture to the determine the level of extracellular enzyme activity in the permeate as an indication of biofouling of the membrane.